Sun-dial gnomon.



WITNESSES: A

' F. J. DICK.

SUN DIAL GNOMON.

APPLICATION FILED JULY 16, 1908.

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Patented Dec.20, 1910.

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r F. J. 1110K. K SUN DIAL GNOMON.

APPLIUATIN FILED JULY 16, 1908.

' 978,859. Patented Dec.20,.1910.

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WEST EAST F1 cfa-fs UNITED STATES yPATENT oEEiCE.

FREDERICK J. DICK, OF POINT LOMA, CALIFORNIA, ASSIGNOR T0 KATHERINETINGLEY, 0F POINT LOMA, CALIFORNIA.

SUN-DIAL GNOMON.

Specification of Letters Patent.

Patented Dec. 20, 1910.

Application led July 16, 1908. Serial No. 443,920.

To all 'whom 'it may concern.'

Be it known that I, FREDERICK J CHN DICK,

a subject of His Majesty the King of GreatV Britain, residing` at PointLoma, in the county of San Diego and State of Califor nia, have inventedcertain new and useful Improvements in Sun-Dial Gnomons, of which thefollowing is a specification.

The object of my invention is to provide al means of ascertaining thecorrect clock time in use at any station, by mere inspection of theshadow of my improved gnomon cast by the sun, without at any timetouching or manipulating the sundial, and without having recourse tocorrections or calculations. I attain this improvement by the generalarrangements illustrated in the accompanying drawings, in which- Figure1 is a side view of my improved gnomon, which is throughout circular incross section. Fig. 2 is a perspective view of this gnomon, mounted in asuitable frame containing a cylindrically-shaped surface whose a-Xis isthat of the gnomon, on which surface is delineated an hour-line suitablysubdivided. Fig. 3 illustrates the shadow of my improved gnomon crossingthe hourline. Fig. 4, on the same scale as Fig. l, shows the curve ofthe equation of time., cor rected for the suns semi-diameter. Fig. 5 isa longitudinal section of the two surfaces of revolution generated bythe rotation of the curve in Fig. 4 upon its line of abscissae, or polaraxial line.

The dimensions marked in Fig. l are such as would be used in connectionwith an hourline having a radius of nine and one-sixth units. This givestwo-fifths of a unit for every ten minutes on the hour-line. The unitemployed in the actual drawings, Figs. l, 3. 4 and 5, is onel inch.The..dimensions in Fig. l are determined as hereinafter eX- plained.

In Fig. 2, A is the improved lgnomon which is mounted so that its axislies in the plane of the meridian; with its north or small end elevatedif in the northern hemisphere, or depressed if in the southern. at anangle equal to the latitude of the station. B is the cylindricalsurface, inclosed within the framework E, on which surface is marked thehour-line D in a plane centrally at right angles to the aXis of thegnomon,or in other words in the plane of the eouinoctial. C is a strongsemi-cylinder of glass inclosing and protecting the dial both fromatmospheric influences and from being tampered with; for once erected, asundial furnished with this improved gnomon need never be touched.

The abscissae measured from the central transverse line, or equinoctialplane, in Fig. 4, are equal to the tangents of the varioussun-declinations multiplied by the radius of the hour-line. Theordinates to the curve are practically those of the equation of time, onthe scale of measurement of thehour-line, plus a distance equal to oneminute of time measured on the hour-line. This is because the definededge of the shadow is always one minute nearer the center of the shadowthan it would be if the sun were only a point, instead of occupying, asit does 0 32 of arc. The curve, thus obtained, of Fig. 4 being rotatedupon the line of abscissae as an axis, the double curves of Fig. 5result, representing the longitudinal section of tw'o surfaces ofrevolution. The problem now is, to construct a solid which will producea shadow, when at the varying angles due to the suns northernly orsouthernly declinations, such that, in the immediate vicinity of thehour line, it will clearly indicate two sets of curves, and in suchmanner that the definite edge of one or other of them shall intersectkthe hour-line at the proper point to give the correct time. Theprinciple by which this is attained may be expressed by imagining aseries of thin flat circular disks strung at intervals on a centralwire, Athe disks being also pierced centrally by a couple of spindlesend to end of smaller sectional area. The outer curves of Fig. 5 wouldenvelop the disks, and the'inner curves the two solid spindles. Theshadow thrown by such an object would obviously reproduce the generaloutlines ofboth sets of curves in Fig. 5. Reference to Fig. 1 showsthat, practically, the supposed thin disks, are united to the supposedinner-spindles by sloping surfaces, without interfering with thedesigned effect, as regards the shadow.` Thus the outline of the curveinclosing the supposed disks is indicated by a series of ridges on theshadow, and that of the supposed inner spindles by a series ofdepressions or hollows on the shadow.

Having due regard to the fact that the shadow of any circular crosssection of the gnomon, when the sun has a declination other than zero,will always be an ellipse, the dimensions shown in Fig. 1 result, for anhour-line radius of nine and one-sixth units. For any other radius, allthe dimensions, `whether longitudinal or transverse, change in the sameproportion, so that the instrument can readily be constructed of anyconvenient size. The dimensions given in Fig. 1 are thus a necessaryguide to the practical construction of a gnomon which will fulfil theconditions above indicated. In Fig. 3 is shown the actual definite edgesof the shadow outline, in the vicinity of the hour-line, produced by agnomon constructed in accordance with these dimensions, whenever thesuns declination happens to be about 14O south. The wavy lines S S inFig. 3 show the appearance of this improved gnomons definite shadowrelatively to the hour-line D, .at a certain moment on February 9th, orat a certain moment on November 3rd. The plane of the meridian is shownby the dotted line M M. For the purpose of clearly explaining` how it isthat the correct clock time is shown, it is purposely assumed i in Fig.3 that the sundial is situated at a place whose longitude is fivedegrees to the eastward of some standard time meridian, and wherestandard time is used. Hence the XII, or noon-point, is here showntwenty minutes to the east of the meridian line M M. In other words, thehours and their subdivisions are here shown, relatively to the meridianplane, as suited for places having` longitudes, for example of 700, 85,1000, or I. 115O west of Greenwich, and which use eastl ern, central,mountain, or Pacific time, respectively. For places using local meantime the XII-point would coincide with the meridian; and for placeshaving other longitudes than those of standard time meridians, and usingstandard time, the XII-point would be situated east or west of themeridian line M M, according to the same rule as is illustrated in Fig.3.

The method of using a sundial furnished with my improved gnomon isindicated by the following directions, which are intended to be markedon the surface B, Fig. 2, or other convenient part of the sundial Dec.27 to Mar. 21 read profile of easterly indentations of shadow.

Mar. 22 to Apr. 13 read profile of easterly protuberances of shadow.

Apr. 19 to J un. 12 read prole of westerly indentations of shadow.

Jun. 18 to Aug. 30 read profile of easterly protuberances of shadow.

Sep. 4 to Sep. 23 read profile of westerly indentations of shadow.

Sep. 24 to Dec. 23 read prole of westerly protuberances of shadow.

Read profile means: read, on the hourline, the point where an imaginarycurve drawn through the easterly (or westerly) indentations (orprotuberances, as the case may be) of the gnomon-shadow would cut t-hehour line.

In Fig. 3, assuming it to be the month of February, we read the profileof easterly indentations of shadow,and the time shown is therefore 11.34a. m., standard time. As-

suming it to be the month of November, we

read the profile of westerly protuberances of shadow, and the time shownis therefore 11.0371- a. m., standard time.

Vhat I claim as my invention and desire to secure by Letters Patent is-A sundial-gnomon permanently fixed and formed with a series oftransverse tlutings so designed that the sun throws across the hour-lineof the sundial a shadow indicating the profiles or outlines of twoindependent sets of curves of such a nature that the correct clock timecan be read on the hour-line, substantially as described.

In testimony whereof I affix my signature in presence of two witnesses.

FREDERICK J. DICK. litnesses C. TI-rUns'roN, J. FRANK KNOCKE.

